1. Field of the Invention
This invention relates to a method of preparing a silicone elastomer with a paintable surface.
2. Description of the Prior Art
Silicone elastomeric compositions which cure through the reactivity of the acetoxysilicon functionality have been known for some time as illustrated by Bruner in U.S. Pat. No. 3,035,016 and Dupree in U.S. Pat. No. 3,274,145.
Bruner describes acyloxy siloxanes, moisture curing compositions and their preparation. Bruner describes using inert organic solvents to prepare his siloxanes including hydrocarbons such as benzene, toluene, xylene or petroleum ethers; halogenated solvents such as perchloroethylene or chlorobenzene and organic ethers such as diethylether and dibutylether, ketones such as methylisobutylketone and fluid hydroxyl-free siloxanes. Bruner states that the compositions may be kept in the solvent until it is used, particularly when a gummy product is to be employed in coating applications. Bruner also suggests using well-known reinforcing fillers such as fume silicas, silica aerogels, and precipitated silicas; non-reinforcing fillers such as coarse silicas like diatomaceous earth, crushed quartz or metallic oxides such as titania, ferric oxide and zinc oxide and fibrous fillers such as asbestos or glass. Bruner in U.S. Pat. No. 3,077,465 also teaches the use of carboxylic acid salts of metals including the tin salts for improving the curing of the compositions at room temperature.
Dupree describes acyloxy siloxane compositions prepared using siloxane polymers which are partially endblocked with triorganosiloxy units, the remaining endblockers being hydroxyl radicals. Dupree describes the use of fillers such as powdered metals such as aluminum, tin and zinc; powdered silicon, silica, mica, clay and metal oxides such as iron oxide.
Shaw in U.S. Pat. No. 3,701,753 describes organic solvent solutions of a silicone rubber composition containing a silanol-terminated diorganopolysiloxane base polymer with a viscosity of 1,000 to 100,000 centipoise at 25.degree.C. and an organotriacyloxysilane. Shaw teaches that only a few organic solvents have been found suitable which include ethylacetate, pentane, hexane, heptane, mineral spirits, naphtha, xylene, toluene and cyclohexane where cyclohexane is the preferred solvent. Shaw, however, states that ethylacetate, xylene, toluene, normal alcohols, ketones and chlorinated hydrocarbons are unsuitable because they are too hydroscopic to provide shelf stable compositions.
Shaw also describes the use of from 10 to 200 parts filler per 100 parts of the organopolysiloxane polymer. The fillers described are titanium dioxide, lithopone, zinc oxide, zirconium silicate, silica aerogel, iron oxide, diatomaceous earth, calcium carbonate, fume silica, precipitated silica, glass fibers, magnesium oxide, chromic oxide, zirconium oxide, aluminum oxide, crushed quartz, calcined clay, asbestos, carbon, graphite, cork, cotton and synthetic fibers.
In U.S. Pat. No. 3,817,894, Butler et al. describe a commercial silicone rubber bathtub caulk based on an acetoxyfunctional silicone polymer and show the cured product has poor paintability properties with both latex and oil base paint.
From the prior art, it is thus known to prepare acyloxy containing silicone compositions in organic solvent and to use fillers, but it is unexpected that a paintable surface can be obtained from a cured acetoxy containing composition.